The present invention relates to a system for regenerating a particulate trap in an exhaust gas of a diesel engine etc., and in particular to a system for determining/controlling the time of initiation of the regeneration of the particulate trap.
In a conventional regeneration system for a particulate trap (hereinafter abbreviated as a trap), the regeneration of the trap is generally initiated by regeneration means such as an electric heater and a burner when one of the following conditions is satisfied:
(i) When the pressure loss (pressure difference) between the inlet and the outlet of the trap reaches a reference value preset in a memory map having stored therein reference pressure losses in relation to engine conditions such as revolution as a parameter;
(ii) When the quantity of trapped particulates which is estimated from the intake air flow rate of the engine measured by an air flow meter and the pressure loss of the trap reaches a predetermined value;
(iii) When the quantity of trapped particulates indicated by the ratio between the pressure loss of the trap and the pressure loss of a silencer as a fixed wringer provided at the outlet of the trap reaches a predetermined value as disclosed in Japanese Patent Application Laid-open No. 60-108520;
(iv) When the present pressure loss of the trap reaches a trapped pressure loss determined from the gas flow rate further determined from the pressure difference across an inlet valve of the trap when the opening of the inlet valve is fixed in a predetermined range as disclosed in Japanese Patent Application Laid-open No. 63-295815 by this inventor.
It is to be noted that the condition of the initiation of the regeneration of whether or not the integrated value of the number of revolutions of an engine or the running distance of a car reaches a predetermined value should not be practically used in terms of precision since the effect of the engine load is fully neglected.
Such a conventional regeneration system for a particulate trap which determines the initiation time of the regeneration on the basis of the pressure loss of the trap on the above conditions (i).about.(iv), takes no account of the clean state of a trap. Namely, in spite of the variation of the pressure loss under the pre-use condition of traps, the initiation time of the regeneration is uniformly determined assuming that the pressure loss under the clean state is the same for any trap.
Therefore, it is disadvantageous that the quantity of trapped particulates has a variation which provides unpreferable regeneration, resulting in an excessive regeneration which melts the trap and in an incomplete regeneration which leaves particulates.